In the Spatial agro-ecology theme we place crops within the agro-ecological landscape, and study the interactions of crops with populations of other organisms (weeds, pests and pathogens) with emphasis on the spatial and temporal dynamics of these interactions. CSA uses knowledge thus acquired to develop integrated approaches for sustainable weed and pest management, to better understand the ecology and management of invasive species, and to determine the provisioning of ecosystem services.
Invasive tree pathogens are a major threat to the worlds indigenous forests and tree-based industries. Globalization leads to increased connectivity between different parts of the world, allowing new pests to enter, establish and spread at never before seen rates. Recent examples include the fungal pathogen ash-dieback (Hymenoscyphus fraxineus) and the bacterial agent that causes olive decline (Xylella fastidiosa).
Risk managers need tools to predict risk of invasion and prevent damage by taking appropriate action and evaluate beforehand the possible effects of these actions. In this project we will aim to predict the location of first establishment of tree pathogens, using historic establishments.
In this thesis you will crunch, screen and clean large datasets & read relevant literature. You will be using a recently developed methodology to predict hotspots of pathogen establishments and test which drivers explain establishment (trade, tree cover, nurseries etc.). You will encounter the limitations of the available data and will need to find solutions to make your model work.
We are looking for a motivated student that is interested in invasive species, likes to do a desk study using literature and statistics and has an interest in modelling. Proficiency with programming in R and experience with modelling are advised. Having followed Ecological Modelling and Data Analysis in R or other modelling courses is helpful for this thesis.
Bob Douma (email@example.com) and Robbert van den Dool (firstname.lastname@example.org)
With the challenge of reducing pesticide use, early detection and monitoring of crop pests is essential in controlling pest dynamics. Colorado potato beetle is one of the most devastating insect pests in potato crops and its impact on crop damage and subsequent yield loss is expected to increase even further due to climate change. This MSc thesis project aims to explore the feasibility of detecting the beetle and its abundance from the air by using data from high resolution cameras that were mounted on drones. A big data set is available with actual counts on the potatoes over the last growing season (2020).
In this thesis project you will explore the feasibility of detecting and counting beetles from remote sensing images. This may involve the application of advanced machine learning techniques such as deep learning.
We are looking for a motivated student that is interested in this relevant topic. Depending on your interest you can take a more ecologically oriented focus, or a more prediction-oriented focus. In the former, you will analyse the field data in more detail to understand dispersal patterns of the beetle (collection of additional field data is an option). In the latter, you would apply state of the art image analysis techniques on an important agricultural problem, and skills on, or, affinity with remote sensing imaging and machine learning is needed (e.g. the courses data science for ecology, deep learning, machine learning would prepare you for this thesis).
Bob Douma (email@example.com, 0317-482140) and Lammert Kooistra (firstname.lastname@example.org)
Contribution of living landscapes to agricultural ecosystem services: pollination and biological control
Living landscapes support a variety of beneficial insect communities for agricultural ecosystem services such as biological pest control and pollinations, while these valuable services have suffered from intensification of agriculture and simplification of agricultural landscapes. Our study is carrying out over a gradient of landscapes from complex to simplified, aiming to quantify how landscape factors affect pollination services and biological control in oilseed rapes and rice. The study is located in Nanchang City, Jiangxi Province, China
Two projects are available:
1. Landscape diversity and pollination services
Target crop: oilseed rape. Experimental methods: pan traps and pollination exclusive treatments. Study time: March – May 2015
2. Landscape diversity and biological pest control
Target crop: rice. Experimental methods: bait card experiment, cage experiment and blower-vac sampling.
We are looking for students who are interested in erotology and agricultural science, and who are willing to visit China! You will have fun by meeting people and exploring Chinese culture. Accommodation will be arranged and living costs will be covered.
Dr Wopke van der Werf (email@example.com) and Dr Felix Bianchi (firstname.lastname@example.org) Inhoud
Pyrethrum Tanacetum cinerariifolium and some other species in the genus Tanacetum are perennial species that produce pyrethrins that are used as natural pesticides, especially in organic agriculture. The ecological significance of pyrethrin production is known to be both protection of the plant against insects and, as pyrethrin accumulate in flowers and seeds, protection of offspring against fungal attacks. However, Pyrethrum is also insect pollinated probably primarily by thrips and like other flowering plants the flower is designed to attract pollinators. Pollination is known to be poor in general, however. Thus, an interesting combination arises, as flowers are both made to attract pollinators and at the same are loaded with pyrethrins that deter insects. It has been hypothesized that this represents a so-called push-pull strategy by the plant, in which an ecological balance between sufficient reproduction and annual survival is reached. Roughly this idea entails that these flowers are cleverly designed to attract sufficient pollinators but simultaneously deter potential herbivores so that reproductive success is not diminished. Understanding this dynamic is ecologically highly relevant as it leads to better understanding of why flowers are designed the way they are, but is of major agricultural importance as well, because pollination is also correlated to pyrethrin content and therefore economically important.
An experiment was conducted in which different Pyrethrum accessions with unknown variation in Pyrethrin content were grown and were either exposed to thrips or not. Flowers were collected both at the pollination stage (stored in alcohol) and at the ripe stage for seed experiments. The question to be addressed here is if there is correlation between pyrethrin content and the number of thrips on the flowers and also whether there is a relation between the presence of thrips and pollination success. Experiments will be conducted (i) to see whether the presence of thrips has influenced the number of fertile seeds, and (ii) whether the pyrethrin content has affected the thrips numbers. In addition we have a suite of accessions from a wild sister species with a known variation in pyrethrin contents and some distinct differences with pyrethrum. These are growing in a field plot and can be characterized in various ways. Several types of measurements or small experiments are possible.
The project is supvervised by Niels Anten (CSA) en Maarten Jongsma (PRI)
Niels Anten (email@example.com)
Weeds are a serious biotic production constraint in most agricultural production systems. Acting at the same trophic level as the crop, weeds capture resources that cannot anymore be used by the crop. Therefore, leaving weeds uncontrolled will sooner or later lead to considerable reductions in crop yield.
Curative weed control is mainly focussed on weed seedlings and is strongly dominated by the use of herbicides. This heavy reliance on chemical control is considered objectionable because of potential negative side-effects on food safety, public health and the environment. Additionally, cropping systems with a narrow focus on herbicidal control are less sustainable, due to an increased risk regarding the development of herbicide resistance.
Cultural control refers to any adjustment of the general management of the crop that contributes to the regulation of weed populations and reduces the negative impact of weeds on crop production. This preventative approach addresses a variety of life cycle stages and relevant processes, like the weed soil seed bank, seed recruitment, weed seed production and seed predation. Various measures like photo-control, bio-fumigation, mulching, stale seedbeds, transplanting, weed suppressive cultivars and no till systems potentially contribute to this kind of ecological weed management.
The questions that remain are manifold, just to mention a few:
- Which life cycle stage of the weeds can best be tackled?
- How effective and reliable are individual cultural control measures?
- Do the measures combined provide synergistic effects?
- Are weed community changes likely to result from a modified management strategy?
- What is the role of crop rotation in ecological weed management?
Types of research:
- Literature review with follow up analyses of already published data
- Experimental approaches to evaluate individual measures
- Population dynamical models to evaluate control measures and to study changes in weed community composition.
Lammert Bastiaans (firstname.lastname@example.org)
Agricultural production is supported by ecosystem services (pollination, natural pest control, soil processes, etc), because of the presence of beneficial arthropods and other organisms. Intesively used, simplified agricultural landscapes have reduced biodiversity and reduced levels of ecosystem services. We are interested in options for management and landscape design that support the increase of ecosystem services in agro-landscapes. Stakeholders with different interests are involved in this transition of agro-landscapes.
Beneficial arthropods (hover flies, lady beetles, parasitoid wasps, wild bees, etc) need resources like nectar, pollen, shelter and alternative food, found in semi-natural habitats such as road verges, woodlots, ditch banks and flower strips, but also in agricultural fields. We study the relation between the distribution and temporal dynamics of these vital resources for different groups of beneficial arthropods in agro-landscapes. The spatial arrangement and quality of landscape elements (agricultural fields as well as semi-natural habitats) also influence the provisioning of other ecosystem services (such as water purification, biodiversity, recreational value), which are interesting for farmers, and other stakeholders.
In this project we apply different approaches that are integrated in a landscape design and evaluation method (Landscape Images). It includes field work, modelling, workshops with stakeholders, GIS and database analysis, and others. The project focusses on two case study areas: Hoeksche Waard and Flevopolders.
Types of research:
For MSc or BSc thesis work different types of research are possible, including:
- field work (also in winter: impact of tillage practices on hibernation of arthropods)
- GIS and database analysis
- workshops or surveys (depending on phase of the project)
Dr Wopke van der Werf (email@example.com)
Individual plants harbour a dynamic multispecies insect herbivore community. These herbivore communities select on plant defence strategies. These defence strategies consist of a constitutive baseline of defence as well as an induced response to attack. Whereas constitutive defences are costly to maintain but readily available, inducible defences reduce metabolic costs of defence in absence of herbivores and allow plants to tailor defences to the specific herbivore attacker. Inducible defences may have ecological costs as induced resistance to one herbivore may lead to increased attraction and susceptibility to other herbivores. For many plant species, it is unknown which herbivores have the strongest impact on plant fitness, whether each herbivore acts as an independent cost on fitness or whether indirect interactions among herbivores cause plant fitness consequences. For example, the first arriving species may affect the order and timing in which subsequent species arrive. To unravel these relationships large datasets are required which have been collected in the past years. In this thesis you will use statistical approaches to find patterns in the dynamics of insect community composition and seed production of Brassica nigra plants.
The proposed work consists of constructing statistical models to test for patterns in order of arrival and the consequences of the insect community composition on plant fitness, etc. Questions can be tailored to the student’s interest. A good knowledge of insect ecology is needed as well as affinity for statistical analysis and large datasets. Students will be based at CSA and collaborating with Entomology where the dynamic processes of plant-insect communities are studied.
Fundamental and Applied Biology of Insects (ENT-30806) and either Molecular and Evolutionary Ecology or Ecological Aspects of Biointeractions (ENT-30306), and/or Ecological Modelling and Data Analysis in R (CSA-34306).
Bob Douma (CSA, firstname.lastname@example.org) and Erik Poelman (Entomology, email@example.com)
Carabid beetles remove weed seeds in arable land, supporting the biological control of weeds. Many studies have been done on the abundance and diversity of carabids in arable land and their predation on weed seeds. We are currently conducting meta-anayses to identify key factors affecting carabid abundance and elucidate the relationship between carabid abundance and weed seed removal. In experimental studies, carabid abundance is measured with pitfalls which measure not exactly abundance but a metric called “activity density” because the number of beetles trapped depends both on the density of the beetles and their movement activity. Seed removal is usualy quantified using sand papers cards with seeds glued on them, which are then placed in the field for a period of time to allow beetles to remove seeds. In the meta-analysis, we want to related the seed removal from seed cards to the activity density measured in pitfall traps. However, we do not understand very well what relationships we should expect, especially in relation to the number and size of the pitfall traps and seed cards, and the time of exposure of both in the field.
To better understand the relationship between the activity density of carabid beetles as measured with pitfalls and the seed removal measured with seed cards, we want to model the movement process and model seed removal in relation to the density of carabids, their activity (movement rate and frequency distribution of turning angles), and other factors such as the size of seed cards, the behaviour of carabids on and near the seed cards and at edges. We are looking for a student who is interested in individual-based modelling of this process. The model could be developed in netlogo, R, MatLab or other language of preference. The study aims to show how length and time parameters of the carabid trapping and seed removal measurement affect the relationship between both. This provides important basic insight to support the meta-analysis of the relationship between carabid activity density and weed seed removal.
Open for anybody with quantitative skills
Wopke van der Werf (firstname.lastname@example.org) or Bob Douma (email@example.com)
Plant density is a key factor in regulating pest and disease epidemics. According to the resource concentration hypothesis plant density will positively affect density of insects and pathogens. With increasing planting density, microclimate alters, movement between plants becomes easier and plant defenses may be lowered because of increased investment in competition. A qualitative scoring of papers publishing the effects of plant density on the abundance of phytophagous insects showed a positive affect of plant density on host abundance in only ~34% of the studies (Rhainds & English-Loeb, 2003). Others reported as positive effect in ~57% of the studies. As the effect of plant density on pest abundance can be both positive and negative, a better understanding is needed to what determines the relationship between host density and pest abundance. A better understanding on the relative contribution of factors that contribute to disease epidemics as a function of host density is crucial in both managed and natural ecosystems.
Type of work
In this thesis project you will do a quantitative review of the literature (meta-analysis) to investigate the overall relationship between plant density and disease prevalence, and to try uncover factors that affect this relationship. This involves a lot of reading, data, statistics and fun.
I am looking for a motivated student that is interested in this relevant topic, and likes to do a theoretical study using literature and statistics.
Bob Douma (firstname.lastname@example.org, 0317-482140)